Metal oxidizing process



R: F. ALTMAN METAL oxIDIzING PROCESS Filed Feb. 15'," 1963' Y lNvENToR @gy f.' A/man Wim ATFORNEY May 25,1965

United States Patent O 3,185,597 NIE'IAL (DXIDIZING PROCESS Roy F. Altman, Emporium, Pa., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed Feb. 15, 1963, Ser. No. 258,680 4 Claims. (Cl. 148-16) This invention relates to the .treatment of alloys adapted for glass-to-metal sealing and more specifically to the treatment of a chrome-bearing alloy prior to the formation of a surface oxide thereon which is adapted to provide a bond intermediate the glass and the metal alloy.

It is well known that chrome-bearing alloys are particularly adapted for glass-to-metal sealing and a number of such alloys have beendeveloped with specific characteristics which enhance the manufacture of such seals. Among the more important requirements'of such alloys are heat expansion characteristics throughout the usable temperature range which are similar to that of the glass selected and the ability to form a metal oxide layer thereon prior to the glass-to-metal sealing process which is not loose or akey but rather clings tenaciously to the metal.

Several processes for oxidizing a chrome-bearing alloy prior to a glass-to-metal sealing step are Well known and one of such processes is fully described in Kingston U;S. Patent No. 2,371,627. However, it has been found that control and predictability of such an oxidation process is dependent upon the condition of the metal alloy and its surface prior to such a process. Thus, it has been customary to subject the alloy surfaces to acid etching, degreasing, tumbling in grit, and similar cleaning techniques in attempts to provide an uncontaminated surface.

While these techniques have been of considerable aid in preparing the alloy surface for the oxidation process by removing surface contaminants as well as undesirable surface oxide layers, it is believed that a portion of the desired chrome metal is also removed from the surface. Further, it is`believed that the removal of chrome from the surface has a deleterious effect upon subsequent oxidation processes. Thus, processing of the alloy prior to the formation of an oxide layer thereon is an important factor in determining the success of the oxide formation process. Further, prior processes and cleaning techniques were messy, time consuming, costly, and not particularly adapted to automation.

Therefore, it is an object of this invention to enhance the surface of a chrome-bearing alloy in preparation for the oxidation thereof.

IAnother object of this invention is to improve the reliability of an oxide Vformation process for a chromebearing alloy preparatory to the oxidation of the surface thereof. Y

A further object of this invention is to provde an improved process for treating a chrome-bearing alloy preparatory to oxidation of the surface thereof.

A still further object of this invention is to increase the available surface chromium of a chromium-bearing alloy prior to an oxidation process of the alloy surface.

These objects are fullled in one aspect of the invention bythe provision of a reducing atmosphere wherein the chrome-bearing alloy is subjected to an elevated temperature whereupon surface contaminants and undesired surface oxides are removed therefrom. Substantially simultaneously the surface of the alloy is chrome enriched thereby providing a surface especially adapted to the formation of an oxide for bonding the glass to the metal in a glass-to-metalseal. Y

For a better understanding of the present invention, together with other and further objects, advantages, and

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capabilities thereof, reference is made to the following disclosure and appended claims in connection with the accompanying drawing in which:

FIG. 1 illustrates a typical furnace and gas cracking layout for carrying out the present invention.

In the glass-to-metal sealing art, the formation of an oxide layer on the surface of a chrome-bearing alloy prior to the actual sealing process has become a generally accepted procedure. The thickness and adherence of this oxide layer is believed to be dependent upon the amount of chrome available at the alloy surface which in turn is dependent upon the treatment of the alloy prior to the oxide formation process. Thus, the glass-to-rnetal seal is directly affected by the alloy treatment prior to the oxide layer formation process.

Additionally, in the treatment or process to be described, it is believed that the chrome in a chrome-bearing alloy subjected to the proper combination of time, temperature, and atmosphere mgrates to the surface of the alloy whereat it may be subsequently oxidized to the desired chromium oxide. Further, this same process provides an alloy surface substantially free of undesirable and unwanted contaminants and oxides. Moreover, chrome-bearing alloys subjected to this treatment prior to the oxide formation process have an oxide layer after the oxide formation process which is more uniform and more tenacious than any obtainable by previously known methods.

Although there are numerous chrome-bearing alloys having thermal coefficients of expansion especially adapted for glass-to-metal seals to which this treatment or process is applicable, one specific example is disclosed in Patent No. 2,394,919, issued to W. E. Kingston. This particular alloy is comprised of approximately 42 percent nickel, 4 8 percent chromium, and the balance substantially iron. Other appropriate examples are Fernichrome consisting of approximately 37 percent iron, 30 percent nickel, 25 percent cobalt, and 8 percent chromium, and Allegheny #55 consisting of approximately 0.35 percent carbon, 1.0 percent manganese, 0.6 percent silicon (max), 23-30 percent chromium, 0.6 percent nickel, and the balance iron. It is to be understood that these examples are not to be construed as limitations but rather as examples of chrome-bearing alloys which may be treated by the present process prior to the oxide formation process.

One example of a furnace and gas-cracking apparatus found especially applicable for execution of the process or treatment of this invent-ion is fully described in Patent No. 2,398,012., issued to D. R. Kiser. However, numerous types of commercially available equipment wherein raw gases are cracked and the resultant atmosphere used in a heating furnace Iare also appropriate.

` Briefly stated, the gas-cracking apparatus of the abovementioned patent provides for incomplete combustion of raw gases in the presence of a catalyst whereby an .atmosphere is produced consisting essentially yof CO, CO2, H2, H2O, and N2. The precentage composition of each constituent in the resultant atmosphere is determined by the raw gas selected, the catalyst in the gas-cracking apparatus, and the air to gas ratio admitted to the apparatus. Further, due to the ease with which adjustments may be made, the atmosphere is most frequently controlled by varying the'air to gas ratio.

Referring to the drawing, there is shown in schematic forma furnace and gas-cracking apparatus applicable to the present process having a gas inlet 1 and an air inlet 2 into which are admitted raw gas and air. The admitted air an-d gas flow through appropriate flow meters 3A and valves 3 to an air gas mixer 4 of any well-known construction for mixing gases and thence 'to an atmosateneo? phere controller 5. In this controller 5 is contained a suitable catalyst for the selected gases as is common in many forms of commercial gas-cracking apparatus. Thus, varying the amount of kiiow through the flow meters 3A by means of the valves 3 provides readily accessible means for selectingV the resultant atmosphere flowing from the atmosphere controller 5. This resultant atmosphere is passed through an applicable cooling chamber 6 and into the reducing furnace consisting of a muliie 7 surrounded by a heating means 8 such as a gas or electric heater. The muie 7 is preferably horizontal and the atmosphere passes from the cooling chamber 6 into the muiiie through inlets 9 and 10. Aninclined inlet 11 and an inclined outlet 12, 4preferably surrounded by a water jacket 13, are connected to the muftie 7 and an endless conveyor belt 14 passes therethrough. Exhaust vents 15 and 16 are preferably provided at the inlet and outlet ends of .the furnace.

Thus, raw gases suc-h as coke-oven gas, propane, butane, and preferably natural gases are admitted to the gas-cracking apparatus through inlet 1 in a predetermined air Ito gas ratio wherein a desired and known atmosphere is obtained. This atmosphere is conducted to a heating furnace having appropriate temperature controls and through which a supply of parts to be processed are conveyed on an endless belt and at a controlled speed.

Preparatory to carrying out the process, the air to gas ratio introduced into the gas cracker is adjusted to provide a desired atmosphere in the furnace. Further, it has been found that an air to gas ratio in the range of 3/1 to 8/1 provides the necessary amounts of water va'- por, hydrogen, and carbon monoxide required to form a very thin and r-rnly attached oxide layer on the parts while removing the undesired contaminants and gases therefrom. More specifically, an air to gas ratio of 3/ 1 provides an atmosphere of about 30 percent H2, 15 percent CO, 5 perecent CO2 and 50 percent N2 at a water vapor dew point of 70 F. while an 8/ 1 air to gas ratio has approximately 8 percent H2, 6 percent CO, 6 percent CO2, and S0 percent N2 at a water vapor dew point of 70 In the process, the chrome-bearing alloy parts are placed `in a container of metal tray which is conveyed through the furnace on the endless belt. The parts enter the inclined tube and remain `therein for a period of approximately to 25 minutes. This period is adjustable and determined by the rate of travel of the endless belt. While in the inclined tube, a iiow of the predeltermined desirable reducing atmosphere which is maintained at a temperature below 200 F., preferably 175 F., passes over the parts and flushes the air and gases not only from the parts but from the tube as` Well.

Upon leaving the inclined tube, the parts enter the inutile which is maintained at a constant temperature in the range of 1600 F. to 2000 F. and remain there for a period of 10 to 15 minutes. While in this reducing atmosphere, the remaining contaminants or undesirable oxides are removed from the surface of the alloy. Further, it is believed that herein the chrome in the chromebearing alloy migrates to the surface of the alloy thereby providing a chrome-enriched surface especially adapted to provide an oxidized surface when subjected to further processing. Additionally, herein a thin but extremely adherent oxide believed to consist essentially of chromium oxide is formed on the alloy surface.

Subsequently, the parts are conveyed from the muie into the second inclined tube and remain there for a period of 10 to 25 minutes and are Once more iiushed by the above-mentioned atmosphere which is maintained at -a temperature below 200 F. and preferably at approximately 175 F. During this period the parts are sufficiently cooled to permit ease of handling and resistance to further oxide formation thereon when the parts leave the furnace and are ready for the subsequent oxidation process.

As a specific example of the process, natural gas having a specific gravity of 0.64 and a B.t.u. content of 1040 was fed to the above-mentioned gas cracker at an air to gas ratio of 6 to 1. Thus, a furnace atmosphere was provided having approximately 14.0 percent H2, 10.0 percent CO, 5.0 percent CO2, and 71.0 percent N2 at a water vapor dew point of 70 F.

Into this atmosphere a plurality of small cup-shaped parts of an alloy such as disclosed in Patent No. 2,394,919 above were conducted by means of the endless belt Whereon they were disposed within metal trays. At a belt speed of 8 inches per minute, the parts remained within the inclined tube for approximately Va 16 minute period whereat the atmosphere which was maintained at a temperature of 175 F. flowed over the parts and removed the gases adhering thereto.

Upon leaving the inclined tube the parts entered the muie and remained there for a period of approximately 11 minutes during which time the atmosphere was maintained at a temperature of approximately 1900 F. From the mufiie the endless belt conveyed the parts through the second inclined tube to a discharge area whereat they were available for subsequent oxidation processes. This second inclined tube was maintained at a temperature of approximately 175 F. by means of ka water cooled jacket and the parts remained therein for approximately 16 minutes.

Among the many advantages of the. above-described processing over previous prior treatments of a chromebearing alloy are the improved adherence and resistance to sealing or iiaking of the subsequently formed oxide layer. Further, alloys which would otherwise have a lo-ose and non-uniform final oxide layer may now be provided with a uniform `and adherent oxide layer Vif .subjected to 4the above-mentioned treatment prior to a subsequent -oxidation process. Addi-tionally, this prior processing permits the formation of a final oxide layer having a uniformity and tenacity previously unobtainable. Moreover, this prior processing provides alloy surfaces whereon an oxide layer may be formed with a consistency and repeatability which has thus far been unknown.

While there has been shown and described what is at present considered the preferredembodiment of the invention, it will be obvious to those skilled in the art that various changes and, modifications may -be made therein without departing from the invention asV defined by the appended claims.

What is claimed is: 1. A process for treating a chrome-bearing alloy containing surface occluded gases and contaminants prior to the `formation of a iinal surface oxide thereon, said final surface oxide formed to provide an intermediate bond in Ia glass-to-metal seal, comprising the steps of flowing a reducing atmosphere over said alloy at a temperature of less than 200 F. for a period ranging from l0 to 25 minutes, said atmosphere consisting essentially of the cracked constituents of a combustible gas including CO and H2 in an air to gas ratio substantially between 3:1 and 8:1 whereby all adherent gases are flushed from the alloy;

subjecting said alloy to said atmosphere at a temperature in the range of approximately 1600 F. to 200 F. to remove occluded gases and contaminants and cause migration of chrome to said alloy surface; and

cooling said alloy while owing said atmoshpere thereover at a temperature below 200 F.

2. A process yfor treating a chrome-bearing alloy containing surface occluded gases and contaminants prior to the `formation of a final surface oxide thereon, said final surface oxide formed to provide an intermediate bond in a glass-to-metal seal, comprising the steps of iiowing a reducing atmosphere over said `alloy at a temperature of less than '200 F. for a period ranging from 10 to 25 minutes, said reducing atmosphere 5 having `an approximate range between 30 percent H2, 15 percent CO, 5 percent CO2, and 50 percent N2 at a water vapor dew point of 70 F. and 8 percent H2, 6 percent CO, 6 percent CO2, and 80 percent N2 `at a water vapor dew point of 70 F., said alloy consisting essentially of approximately 42 percent nickel, 4 to 8 percent chromium, and the balance substantially iron;

subjecting ysaid alloy to said atmosphere at a temperature in the range of approximately l600 F. to 2000 F. to remove occluded gases and contaminants and cause migration of chrome to said alloy surface; and

cooling said al1-oy While owing said atmosphere thereover at a temperature below 200 F. 3. A process for treating -a chrome-bearing alloy containing su-race occ-lulded gases land contaminants prior to the formation of la final surface oxide thereon, said in-al surface oxide formed to provide an intermediate bond in a glass-tO-metal seal, comprising the steps of flowing a reducing atmosphere over said alloy rat a temperature of less than l200 F. for a period rang- Iing lfrom l -t-o 25 minutes, said reducing Iatmosphere having an approximate range Ibetween 30 perce-nt H2, `15 percent CO, 5 percent CO2, and 50 percent N2 at `a water vapor dew point of 70 AF. 'and 8 percent H2, 6 percent CO, 6 percent CO2, yand 80 percent N2 at a water vap or dew point of 70 F.;

subjecting said alloy to lsaid atmosphere at a temperature yin the range of approximately 1600 F. to2000 F. to remove iocclfuded gases land contaminants and cause migration .of chrome to said alloy surface; and cooling Isai-d 'alloy while flowing said atmosphere there- 'over at `a temperature below 200 F. 4. A process for treating la chrome-bearing all-oy containing surface occluded -gases Iand contaminants prior to the formation of ka Iiinal surface oxide thereon, said nal surface Ioxide lformed to provide an intermediate bond ina glass-to-metal seal, comprising the lsteps of flowing a reducing atmosphere over said alloy at a temperature of less than 200 F. for .a period ranging from 10 to 25 minutes, said atmosphere consisting essentially of the cracked constituents of -a cornbusti'ole gas including CO and H2 in an air to gas Vratio substantial-ly between 3:1 and 8:1 to remove said oocluded gases and contaminants, said 'alloy consisting essentially of approximately 42 percent nickel, 4 to 8 percent chromium, and the balance s-ubstantially entirely iron; subject-ing said alloy to said atmosphere Iat a temperature in the range of :approximately 1600 F. to 2000 F. to remove occluded Vgases and icontaminant-s and oause migration of chrome to said alloy surface; and cooling said alloy while owing said atmosphere thereover at la temperature below 200 F.

References Cited by the Examiner UNITED STATES PATENTS 2,269,943 l/42 Kiser 148-16 DAVID L. RECK, Primm Examiner.

UNITED STATES PATENT oEEICE CERTIFICATE OF CGRRECTION Patent No. 3,185,5297 May Z5, 1965 Roy F. Altman It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 63, for "200 F," read 2000o FO D Signed and Sealed this 21st day of December 1965e (SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Commissioner of Patents TAttesting Officer 

1. A PROCESS FOR TREATING A CHROME-BEARING ALLOY CONTAINING SURFACE OCCLUDED GASES AND CONTAMINANTS PRIOR TO THE FORMATION OF A FINAL SURFACE OXIDE THEREON, SAID FINAL SURFACE OXIDE FORMED TO PROVIDE AN INTERMEDIATE BOND IN A GLASS-TO-METAL SEAL, COMPRISING THE STEPS OF FLOWING A REDUCING ATMOSPHERE OVER SAID ALLOY AT A TEMPERATURE OF LESS THAN 200*F. FOR A PERIOD RANGING FROM 10 TO 25 MINUTES, SAID ATMOSPHERE CONSISTING ESSENTIALLY OF THE CRACKED CONSTITUENTS OF A COMBUSTIBLE GAS INCLUDING CO AND H2 IN AN AIR TO GAS RATIO SUBSTANTIALLY BETWEEN 3:1 AND 8:1 WHEREBY ALL ADHERENT GASES ARE FLUSHED FROM THE ALLOY; SUBJECTING SAID ALLOY TO SAID ATMOSPHERE AT A TEMPERATURE IN THE RANGE OF APPROXIMATELY 1600*F. TO 200*F. TO REMOVE OCCLUDED GASES AND CONTAMINANTS AND CAUSE MIGRATION OF CHRFOME TO SAID ALLOY SURFACE; AND COOLING SAID ALLOY WHILE FLOWING SAID ATMOSPHERE THEREOVER AT A TEMPERATURE BELOW 200*F. 